Generally the discharge voltage of an alkaline cell such as a nickle-zinc cell, an alkali maganese cell, a silver oxide cell or a silver peroxide cell remains substantially constant from the beginning of discharge until almost the end of the life of a cell when the active material is completely used up. It is hence extremely difficult to provide any advance warning that a cell is approaching the end of its useful life. As a result it is difficult to know when the cell should be replaced. In case a conventional alkaline cell is used in an extremely important device, such as an artifical pacemaker for the heart which keeps a patient alive, the cell is changed after a predetermined constant time from the point of view of safety even though the cell is still able to continue to work. It would be desirable to continue using the cell for a longer period of time but this cannot be done for safety reasons.